GENUS OXYTRICHA. 787 



periphery ; anal styles large, but not reaching to the posterior extremity of 

 the body. Length 1-144". Hab. — Fresh water. 



Oxjrtricha fallax, Stein. Pl. XLV. Fig. 7. 

 Body ovate, flattened, two and a half times as long as broad, rounded 

 and widest posteriorly, tapering towards and bluntly pointed at the 

 anterior end ; peristome-field wide, extending backwards nearly to the 

 centre of the body ; its reflected inner border ciliate, curved to the left at 

 its anterior extremity ; ventral setae represented by a few scattered styles ; 

 marginal setae forming a continuous projecting fringe, longest towards the 

 posterior extremity ; three only of the anal styles produced beyond the 

 posterior margin. Length 1-168" to 1-144". Hab. — Fresh water. 



Oxytricha platystoma, Ehr. sp. Pl. XLV. Figs. 8 and 9. 



Body elongate, obovate, two and a half times as long as broad, widest 

 towards the anterior extremity, gradually tapering thence to the rounded 

 but narrowest posterior end ; peristome-field deeply excavate, helicoidal, 

 not extending to the centre of the body, its reflected inner border curved 

 inwards to the left in a spiral manner, bearing a row of fine pre-oral cilia 

 and an undulating membrane ; ventral seta: five in number, marginal series 

 forming an uninterrupted, prominent peripheral fringe, two of the anal styles 

 only projecting a slight way beyond the posterior body-margin. 



This species is identical with the Oxytricha platystoma of Ehrenberg and .Stein. 

 The elegant helicoidal contour of the peristome-field distinguishes it from all the 

 preceding species of this genus, and is at the same time so deeply cut as to show 

 clearly through from the dorsal aspect. Diesing * has proposed to separate hoth this 

 and O. ferrugima from the ordinary Oxytrichff, and to create for them the new 

 generic title of Steinia ; but in face of the more comprehensive partitioning of the 

 genus Oxytricha by Wrzesniowski and Sterki, as here adopted, the further generic 

 separation of these two types does not at present appear desirable. 



Ox3rtricha micans, Eng. 



Body highly contractile; anal styles slender, eight to ten in number, those 

 towards the right-hand side being largest and most prominent ; shape of the 

 body and disposition of the other styles and setae agreeing with that of 

 Oxytriclia pdlionclla. Length 1-300". Hab. — Freshwater. 



Oxytricha aeruginosa, Wrz. Pl. XLIV. Figs. 19 and 20. 



Body very flexible, slightly contractile, elongate-elliptical, about three 

 and a half times as long as broad, the two extremities rounded, the anterior 

 one slightly narrower and curved somewhat to the left ; peristome-field 

 extending backwards to a distance of a little over one-fourth of the length 

 of the entire body ; three uncinate frontal styles and three or four frontal 

 setae ; ventral setae five in number, two situated immediately behind the 

 peristome, one central, and the other two adjacent to the anal styles ; anal 

 styles five in number, slender, and not projecting beyond the posterior 



* ' Revision der Prothelminthen,' 1866. 



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